Preheat an oven to 375 F. Grease a shallow, oven-safe pan and set aside. 

Split the breasts and pound to ½ inch thickness.  

Slice chicken in the middle to open a pocket for stuffing. 

Drizzle half the balsamic vinegar over the sliced mozzarella to absorb. 

Fill each breast equally with tomato, mozzarella and basil. Season the with salt and pepper.

Preheat a cast-iron skillet and add half the avocado oil. Using tongs, sear chicken breasts for 2-3 minutes on each side to brown. 

Place chicken in shallow baking dish. Drizzle with remaining oil and vinegar. Bake for 10-15 minutes, or until internal temperature reaches 165 F.

Serve.